This invention relates to a method for sealing a filter element in a filter cartridge and filter devices produced therefrom.
Filter cartridges are used with a variety of types of filtration media, typically membranes for sterile filtration and sample preparation. The present invention provides an improved method for sealing a filter element in a filter cartridge by overmolding. The present method for overmolding filter cartridges results in a less expensive and improved filter cartridge.
One problem is that currently, a different sized filter cartridge overmold is needed for each different size of filter disk. Needing an overmold for each size of filter disk, in addition to the molds needed to create the two support halves of the filter cartridge, is expensive. Such overmolds are necessary because in the prior art devices the outer edge of the filter housing, the two support pieces being coupled with an overmold, is used to secure the outer edge of the filter sheet to prevent leakage. Indeed, it follows that the prior art filter housing circumference had to be substantially equivalent to the circumference of the filter sheet or media.
For instance, U.S. Pat. No. 4,113,627 discloses a method for hermetically sealing a membrane in filter devices, e. g. filter cartridges. Specifically, it discloses a method comprising the steps of molding a thermoplastic filter support element which has the filtrate passing aperture formed therein, aligning the filter element over the aperture and the adjacent surface portions of the support, applying pressure to the filter element and the adjacent surface portions of the support to capture the edge of the filter element against the support and to form the integral seal between the support and the filter element.
In addition to the above mentioned problem, prior art filter cartridges may burst when subjected to significant pressure. Such bursting may be due to the failure to properly secure the support portions to each other. Such bursting may also be a result of the limitations of the prior art design of such filter cartridges.
The method of the present invention allows for a single overmold to be used to manufacture filter cartridges that can contain different diameters of filter disks. The present invention also provides an overmolding method that produces a complete filter cartridge that is less likely to burst under conditions that would make a prior art device burst.
The present invention provides a method for sealing a filter element in a filter cartridge or filter unit, comprising the steps of:
molding a thermoplastic support or housing in two parts, one first support part and one second support part for the filter element, each support part having at least one fluid flow passageway and said first support part having formed therein at least one overmold flow passageway,
aligning the filter element between the first support part and the second support part of the thermoplastic support or housing so that the filter element covers the fluid flow passageway(s) and so that its periphery is adjacent to the overmold flow passageway(s) and adjacent to the surface portions of the two support parts of the support or housing,
holding the filter element in position on the support or housing and,
injection molding a compatible thermoplastic material that flows over at least a portion of the periphery of the filter element and through the overmold flow passageway(s) such that an integral sealing member between the two support parts of the support or housing and the filter element is formed.
The present invention also provides a method for hermetically sealing a filter element, the method comprising the steps of:
molding a thermoplastic support or housing for the filter element between two mold halves, said thermoplastic support or housing being realized as first and second support parts which respectively have at least one opening inlet and one opening outlet for the passage of a fluid and said support or housing having at least one aperture For the passage of an overmold material,
removing one of the mold halves to expose the surface of the first support part on which the filter element is to be located,
aligning the filter element so that it covers the at least one opening inlet and one opening outlet for the passage of a fluid, so that the filter element is adjacent to the surface portions of the first support part and the filter element""s periphery is adjacent to the at least one overmold flow passageway,
placing a new mold half containing the second support part over said first support part, the filter element and the remaining original mold half, the new mold half having portions which contact and apply pressure to the filter element near the edge of the overmold flow passageway(s), the new mold half and the second support part forming a channel along the periphery of the filter element and a portion of the internal surface of the first support part in the first mold half,
injection molding a compatible thermoplastic material into the channel that flows along the periphery of the filter element and against the internal surface of the first support part and through at the least one overmold aperture to the second support part to form an integral sealing member between the said two support parts, the filter element and the compatible thermoplastic material, and
separating the mold halves and ejecting the complete support or housing and its integral filter element.
The present invention further provides a filter unit for removing contaminants from a fluid stream, comprising:
a thermoplastic support member or housing, a porous filter element and a thermoplastic overmold sealing member,
said thermoplastic support member or housing being formed of a first support part and a second support part, each having at least one fluid flow passageway, and at least one thermoplastic overmold passageway,
said filter element extending over said fluid flow passageway(s), its periphery adjacent to at least one thermoplastic overmold passageway and secured to said thermoplastic first and second support parts by said thermoplastic overmold scaling member also being disposed through the thermoplastic overmold passageway(s).
It is an object of the present invention to allow different diameter membranes to be molded into filter unit or cartridges using the same tool.
It is another object of the present invention to reduce the dead volume of filter unit (filter cartridges).
It is another object of the present invention to produce a filter unit or cartridge that can withstand higher pressures than those currently available.
It is another object of the present invention to maintain the integrity of membranes (filter elements) used in filter units or cartridges by sealing them with a thermoplastic overmold rather than being pinched by a filter support or supports.
It is another object of the present invention to provide thermoplastic overmold passageways that allow the thermoplastic overmold material to flow over the periphery of the membrane and onto the support to provide improved pressure performance.
It is another object of the present invention to provide a membrane support design that assists in avoiding membrane obturation when a soft male luer part is connected to the cartridge or filter unit inlet.
It is another object of the present invention to have superior housing capability by reducing the flexion in comparison with the prior art.
It is another object of the present invention to reduce the cost of manufacturing as well as the time needed to manufacture.